Adjustable reference voltage unit



Oct. 18, 1955 E. H. DINGER ETAL 2,

ADJUSTABLE REFERENCE VOLTAGE UNIT Filed Oct. 10, 1952 3 Sheets-Sheet 1 3 groom 4 OUTPUT VOLTAGE 7a a OUTPUT VOLTAGE M 7 :1?)

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Edward H. Dingew;

Walter Mike\soh,

by W i M Their Attorn e' 2 -100 VDC Oct. 18, 1955 DINGER ETAL 2,721,262

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Walter Mikeflsoh,

heir Attorney.

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Their Attorney.

w u w w w u .w u m W0(FJQ FDlL-DO United States Patent ADJUSTABLE REFERENCE VOLTAGE UNIT Edward H. Dinger and Walter Mikelson, Schenectady,

N. Y., assignors to General Electric Company, a corporation of New York Application October 10, 1952, Serial No. 314,133 19 Claims. (Cl. 250-47 This invention relates to adjustable reference voltage units of the type which is particularly useful in electric motor control systems in which the speed of the motor is maintained at a value corresponding to the value of a preset reference voltage.

In such motor control systems, means such as a potentiometer is provided for enabling an operator to adjust the reference voltage to a higher or lower value and thereby effect an acceleration or deceleration of the motor to a corresponding higher or lower speed. A manual adjustment of the potentiometer requiring a wide change in speed may be made in a very brief interval of time; e. g., a fraction of a second. If the speed of a motor driving a load such as a paper-making machine were permitted to change as abruptly as the potentiometer may be adjusted by the operator, high peak currents would flow in the motor windings and the resulting torque peaks would damage the product of the machine.

In order to avoid excessive transient currents in the windings of the controlled motor, capacitor charging and discharging circuits supplied from a direct source have been incorporated in reference voltage units for limiting the rate of change of the reference voltage to a moderate value irrespective of the rapidity with which the operator makes the adjustment, such a unit being described and claimed in Patent No. 2,546,799 to Thatcher. However, such reference voltage units leave something to be desired in that the rate of change of reference voltage produced in response to small incremental movements of the slider of the potentiometer varies widely with the initial position of the slider because of the varying opposing voltages of the capacitor. Accordingly, an object of the invention is the provision of an adjustable reference voltage unit in which the rate of change of reference voltage for small incremental movements of the slider is the same irrespective of the initial position of the slider.

Another object of the invention is to provide an adjustable reference voltage unit in which the rate of change of reference voltage remains substantially constant during any period of acceleration or deceleration of the motor.

A still further object of the invention is the provision of a reference voltage unit which makes it possible without sacrifice of efiiciency or performance to utilize a substantially smaller capacitor element to produce the desired rate of change of reference voltage than that required in prior adjustable reference voltage units.

In carrying the invention into effect in one form thereof, a direct input voltage is provided, which voltage is adjustable manually to vary the speed of the motor, together with a capacitor and a plurality of electric valves responsive to the difference between the capacitor voltage and the input voltage for charging or discharging the capacitor, so as to hold the capacitor voltage substantially equal to the input voltage.

Charging and discharging circuits are provided in which are included a variable direct voltage that is approximately equal to the varying charge on the capacitor, and a constant voltage of relatively large magnitude to provide an effective or net charging or discharging voltage which is always a constant amount larger than the charge on the capacitor. This constant voltage is effective in the charging or discharging circuit after the charge or discharge has once been initiated in response to a difference between the capacitor voltage and the input voltage, and is instrumental in producing the uniform charging and discharging rates of change of capacitor and output voltage.

For a better and more complete underestanding of the invention, reference should now be had to the following specification and to the accompanying drawing of which:

Fig. 1 is a simple diagrammatical illustration of an embodiment of the invention;

Figs. 2, 3 and 4 are simple diagrammatical sketches of modification; and,

Figs. 5, 6 and 7 are charts of characteristic curves which illustrate the operating advantages of the invention.

Referring now to Fig. 1 of the drawings, terminals 1, 2, 3 and 4 constitute sources of direct voltage of differing magnitudes. For example, the terminal 1 is the positive terminal and the terminal 2 is the negative terminal; the terminals 3 and 4 are intermediate voltage terminals, terminal 4 being the zero or ground voltage terminal. As indicated in Fig. 1, terminals 1 and 3 may be assumed to be 200 volts and volts positive, and terminal 2 to be 100 volts negative with respect to terminal 4, respectively.

The reference voltage unit itself comprises a potentiometer 5, a capacitor 6, a transformer 7 for supplying a constant voltage, such as 200 volts, four electric valves 8, 9, 10 and 11, and resistors 12 and 12a. Although the valves 8, 9, 10 and 11 may be of any suitable type, they are preferably 6SN7GT triode valves with the control electrode of each directly connected to its anode to provide diode operation. Other types of rectifier valves such as 6H6 valves or dry type rectifiers such as selenium or germanium rectifiers may be used if desired.

The potentiometer 5 is connected across the intermediate voltage terminals 3 and 4. It is provided with a movable contact or slider 5a. The voltage which appears across the active portion of the potentiometer, i. e. the portion between the terminal 3 and the slider 5a, is the input voltage.

A terminal 13 and the intermediate voltage terminal 3 constitute the output voltage terminals across which is produced a direct reference voltage which corresponds in magnitude to the input voltage. The upper (as seen in the drawing) terminal of the capacitor 6 is connected to the intermediate voltage terminal 3.

The four electric valves 8, 9, 10 and 11 are connected in a bridge network, that is to say the anodes 8a and 9a are connected together as are the cathodes 10b and 11b, and the cathodes 8b and 9b are respectively connected to the anodes 10a and 11a. The diametrically opposite terminals 14 and 15 of the bridge are respectively connected to the lower terminals of the capacitor 6 and the slider 5a of the potentiometer. Charging and discharging circuits for the capacitor are connected to the remaining terminals 16 and 17 of the bridge. A pair of alternating voltage terminals 18 and 19 are connected to these charging and discharging circuits for supplying a component voltage of constant value thereto. These are preferably the terminals of the secondary Winding 7b of a transformer.

The charging circuit is traced from the lower terminal of the secondary winding 7b to the slider 5a, the active portion of the potentiometer, intermediate voltage terminal 3, capacitor 6, anode a, cathode 10b, resistor 12a and conductor 20 to the upper terminal of the secondary winding. Similarly, the discharging circuit is traced from the upper terminal of the secondary winding 71) through resistor 12, anode 8a, cathode 8b, capacitor 6, terminal 3, active portion of potentiometer and slider 5a to the lower terminal 19 of the secondary winding 7b. When the charging circuit is conducting, the capacitor receives a charge of which the polarity at the upper terminal is positive and that at the lower terminal is negative, as indicated on the drawing.

For the purpose of reproducing the direct voltage across the capacitor 6 at the output terminals 3 and 13 without discharging the capacitor by the control apparatus which is ultimately connected to and supplied from the output terminals, an electric valve 21 is provided which is connected across the direct voltage terminals 1 and 2. It is preferably a three element valve of which the control electrode 21a is connected through a resistor 22 to the lower terminal of the capacitor 6. Although the valve 21 may be of any suitable type, it is preferably a 6SN7GT valve. Its anode 21b is connected to the positive source terminal 1. A resistor 24 is connected in circuit between the cathode 21c and the negative source terminal 2. The valve 21 and the cathode resistor 24 constitute a well-known form of amplifier which is generally referred to as a cathode follower and which operates in a wellunderstood manner. Briefly this cathode follower amplifier produces a voltage amplification between a change in voltage on the grid and a change in voltage on the cathode which is slightly less than unity. It has the property of requiring practically zero grid current for any input voltage within its operating range. Consequently its tendency to discharge the capacitor 6 is negligible, and it is capable of reproducing the voltage on the capacitor 6 at the output terminals 3 and 13 with a high degree of accuracy. In other words, the voltage at the terminal 13 of the cathode follower resistor 24, produced by the voltage drop across the resistor 24, closely follows the voltage of the control electrode 21a, which is connected to the negative terminal of the capacitor 6. Since the positive terminal of the capacitor is connected to the intermediate voltage terminal 3, the direct voltage between terminals 3 and 13 is at all times approximately equal to the capacitor voltage as it varies in response to charge and discharge. However, since a change in the bias voltage is required to vary the conductivity of valve 21 throughout its operating range, the voltage between the output terminals 3 and 13 is not exactly equal to the voltage across the capacitor. As previously stated, the direct voltage between the output terminals 3 and 13 is the reference voltage which in one of the intended applications of the invention is utilized to control timed acceleration and deceleration of a motor in response to changes in the voltage caused by adjustment of the slider 5a. For example, this invention might be used in the motor control system disclosed in Patent 2,507,198- Dinger et al. in place of the unit therein disclosed which produces the reference voltage across the terminals 43a and 24. If used in the system of this patent, the output voltage terminals 3 and 13 of the present invention would be connected to the terminals 43a and 24 of the patent.

With the foregoing description of the elements and their organization, the operation of the reference voltage unit will readily be understood from the following detailed description.

It is assumed that initially the voltages of the points 14 and are equal and that for the purpose of increasing the speed of the motor the slider 5a is suddenly moved downward to a new position on the potentiometer which is more negative than the point 14. Consequently, the point 15 and the anode 11a are made more negative than anode 1011. Therefore, during the first negative halfcycle of the alternating voltage, i. e., the half-cycle in which the voltage at the secondary terminal 19 is positive, valve It will conduct before valve 11 is in readiness and will charge the capacitor positive at its upper terminal and negative at its lower terminal. The charging voltage is made up of a variable direct component and a constant alternating component. The direct component is the difference between the capacitor voltage and the voltage across the active portion of the potentiometer, i. e. between the intermediate voltage terminal 3 and the slider 5a, which difference voltage is positive toward the anode 19a. The alternating component is the voltage across the secondary terminals 18 and 19 which during the negative half-cycle is positive toward the anode 10a. As a result, the valve 10 conducts and charges the capacitor during the entire negative half-cycle. When valve 10 is conducting, the voltage drop between its anode and cathode is approximately zero and thus the voltage of cathode 11b is made equal to the voltage of anode 10a, which is more positive than the voltage of point 15 to which anode 11a is connected. Consequently, during the negative half-cycle, the valve 11 is maintained below cutoff, i. e. non-conducting by conduction in valve 10. Likewise, during the negative half-cycle, the cathodes 8b and 9b are made positive with respect to their anodes 8a and 9a by the alternating voltage, and valves 8 and 9 do not conduct during the negative half-cycle.

At the beginning of the next succeeding positive halfcycle, the alternating voltage has the proper polarity to effect conduction in valves 8 and 9. However, since the cathode 9b is connected to point 15 which is more negative than point 14 to which the cathode 8b is connected, the valve 9 will conduct before valve 8 to provide flow of current through the secondary 7b, resistor 12 and valve 9. Owing to the approximate zero voltage drop between anode 3a and cathode 912, because of the conduction of the valve 9, the voltage of anode 8a is made equal to the voltage of point 15 and thus is made more negative than the cathode 312- As a result, the valve 8 is maintained below cutoff during the positive half-cycle and is thus prevented from conducting and discharging the capacitor.

This action continues during succeeding negative and positive half-cycles, the capacitor being charged only during negative half-cycles, until the voltage across the capacitor equals the voltage across the active portion of the potentiometer, i. e. until the voltage of the point 14 becomes equal to the voltage of point 15. If even the slightest amount of charge is added to the capacitor after this balanced condition has been reached, the point 14 tive half-cycle 11 will conduct to provide flow of current through the secondary 7b, resistor 12a and valve 11. Conduction in valve 11 will make the voltage of cathode 1% equal to the voltage of point 15 and thus more positive than anode 19a with the result that valve 10 will be held below cutoff and prevented from adding to the charge on the capacitor.

If, for the purpose of decreasing the speed of the motor, the slider 5a is moved upward to a point on the potentiometer which is more positive than point 14, the valve 3 conducts and during positive half-cycles of the alternating voltage and discharges the capacitor to reduce the voltage across the capacitor to a value equal to that across the active portion of the potentiometer. The operation is as follows: During the positive half-cycle of the alternating voltage, i. e. the half-cycle in which the secondary terminal 18 is positive, the cathodes 10b and 11b are more positive than the anodes 10a and 11a. and valves 19 and 11 do not conduct. During such positive half-cycles, the anode 8a is made positive with respect to its cathode by the alternating voltage plus the difference of the capacitor voltage and the voltage across the active portion of the potentiometer, which difference voltage is positive toward the anode 8a, whereas the anode 9a has only the alternating voltage applied to it and is therefore less negative than 8a. Thus valve 8 conducts before the valve 9 during positive half-cycles and discharges the capacitor. Owing to the approximately zero voltage drop across valve 8, the voltage of anode 9a is made equal to the voltage of point 14, which is more negative than the point 15 to which the cathode 9b is connected. Thus anode 9a is made more negative than cathode 9b and valve 9 remains non-conducting during the entire positive half-cycle.

The difference between the voltage of the active portion of the potentiometer and the capacitor voltage is negative toward the anode 10a and the valve 10 is therefore not in readiness to conduct at the beginning of the negative half-cycle. The valve 11 however conducts during the entire negative half-cycle and makes the cathode 10b more positive than anode 10a. Thus during negative half-cycles, valve 10 is prevented from conducting and replacing on the capacitor the charge which was removed by the valve 8 in the previous positive half-cycle.

This action continues during succeeding positive and negative half-cycles until the voltage of the capacitor is reduced to equality with the voltage across the active portion of the potentiometer.

If after this balanced condition is reached, the voltage across the capacitor should change even a slight amount and produce a difference between the voltages of points 14 and 15, the effect would be the same as if the difference had been produced by movement of the slider, and the unit would operate in the manner described in the foregoing to restore the balanced condition.

Thus as the direct input voltage between terminal 3 and the slider 5a is adjusted by movement of the slider, the direct voltage across the capacitor changes to become equal to the input voltage after an interval of time, which is determined by the resistance-capacitance constants of the circuit. This direct voltage across the capacitor is reproduced at the output terminals 3 and 13 by cathode follower action of the electric valve 21 and cathode resistor 24.

The relationship between a change in the reference voltage and the time required to effect such a change in response to a rapid movement of the slider from one extreme position to the other is illustrated by the increasing reference voltage curve 25 and the decreasing reference voltage curve 26 of Fig. 5 in which ordinates represent reference voltage and abscissae represent time. It will be noted that these curves are not exactly linear. This non-linearity is the result of the variable direct charging component which is the varying difference between the direct input potentiometer voltage and the capacitor voltage. This difference voltage decreases during the charging period, and as the capacitor voltage approaches its ultimate value of any change, the variable direct component approaches zero. However, the full value of the constant alternating component remains effective in the capacitor charging circuit. As a consequence, the capacitor voltage and therefore the output reference voltage which closely follows the capacitor voltage does not approach its ultimate value as an asymptote, but increases rapidly up to that value at which the direct voltage component is zero. This is illustrated in Fig. 5 in which the curve 25 changes abruptly from an increasing value of voltage to a constant value at the point of its intersection 25a with the ordinate 27 which represents the ultimate value of the reference or capacitor voltage for a movement of the slider to its maximum voltage position.

The presence of the constant alternating component in the charging circuit improves the linearity of the output reference voltage versus time relationship over that which is present in conventional resistance-capacitance charging circuits since the magnitude of the net charging voltage, i. e., the difference between the total voltage acting in the charging direction and the voltage on the capacitor is equal to a constant component plus a variable component. This improvement in linearity is further enhanced by making the constant alternating component large in comparison with the variable component. However, the maximum magnitude of the alternating component is limited by the rating of the electric valves, and the minimum initial value of the direct component is limited by the desired maximum value of the reference voltage.

An advantage of this circuit is that for small incremental changes in the position of the slider in a given direction, the rate of change of the output reference voltage is always substantially uniform regardless of the actual value of the reference voltage at the beginning of the change. The reason for this is that for such small incremental changes, the net charging voltage is always substantially the same, i. e., the sum of the constant relatively large alternating component such as 200 volts, and a relatively small variable component such as S to 15 volts. The magnitude of this constant rate of change of reference voltage for small incremental changes in the position of the slider is equal to the rate of change of the reference voltage in the region of its maximum value, because in this region the net charging voltage is likewise the sum of the constant alternating component and a relatively small variable component. This rate of change is represented graphically in Fig, 5 by the slope of the tangent 25b to the curve 25 in the region of its maximum value. Thus if a small incremental change of the reference voltage is made when the reference voltage has any intermediate value, such, for example, as 30 volts, the rate at which such change takes place will be equal to the rate of change of the voltage in the region of its maximum value. In other words, such small incremental change will take place along a time versus voltage curve 25c having a slope equal to the slope of tangent 25b. This rate of change of reference voltage may be the same for movements of the slider in both directions or different, depending on the values of the resistors 12 and 12a in the discharging and charging circuits respectively. If these resistors are equal, rates of changes for movements in both directions are equal and if different, the rates are different.

Although the constant component of the charging voltage could have been direct voltage, an advantage in the use of alternating voltage is that it makes it possible to use a simple transformer to obtain the electrical isolation required in the circuit. The use of direct current would require the use of a battery which is subject to maintenance or a more complex and more expensive insulated rectifier and filter.

Another advantage of the use of alternating voltage as the major component of the net charging voltage is that the size of the capacitor 6 required to produce any desired rate of change of the reference voltage is reduced approximately percent for given values of resistors 12 and 12a since the alternating charging voltage is effective only approximately 50 percent of the time.

The non-linear effect can be still further reduced by the modification illustrated in Fig. 2 in which the alternating voltage source terminal 19 is disconnected from the slider 5a and is connected to the output terminal 13. As a result of this changed condition, the potentiometer is eliminated from the charging and discharging circuits. In all other respects the modification of Fig. 2 is identical with Fig. 1. Also, the operation of Fig. 2 is substantially identical with that of Fig. l, and consequently a repetitious detailed description is omitted. The differences in operation which result from the changed connection of the alternating voltage terminal are explained in the following description. The charging circuit is traced from the terminal 19 of the secondary winding to the output voltage terminal 13 and from the opposite output voltage terminal 3 through capacitor 6, valve 10, resistor 12a and conductor 20 to terminal 18 of the secondary winding. Similarly, the discharging circuit is traced from'secondary terminal 18 through resistor 12, valve 8, capacitor 6 to output voltage terminal 3 and from the opposite output voltage terminal 13 to terminal 19 of the secondary winding. The total voltage acting in the charging circuit, or in the discharging circuit, is thus seen to be the sum of a constant component which is the alternating voltage of secondary winding 7b and a variable component which is the direct voltage across the output terminals 3 and 13. By cathode follower operation of valve 21 and cathode resistor 24, the voltage across the output terminals is made substantially equal to the voltage across the capacitor. The output voltage diiiers from the capacitor voltage only by the amount of bias voltage between the cathode 21c and the grid 21a required to cause valve 21 to conduct an amount of current such that the resulting voltage drop across resistor 24 will produce a voltage at the cathode which is more positive than the grid voltage by the amount of such bias. This grid bias voltage must vary in order to vary the voltage of the output terminal 13 through its range which for the purpose of illustration has been taken as zero to 100 volts.

;If the direct voltage across the output terminals 3 and 13 was always equal to the capacitor voltage or differed from it by a constant amount, the net charging voltage would be constant and the output reference voltage versus time characteristic would be strictly linear. However, since the voltage at the output terminals 3 and 13 differs slightly from the capacitor voltage by the variable amount of the grid bias voltage of valve 21, the characteristic is not strictly linear. The maximum amount of this variable component is substantially smaller in comparison with the constant alternating component than is the variable component of Fig. 1. Consequently, the output voltage versus time characteristic approaches correspondingly closer to exact linearity than does the output voltage versus time characteristic of Fig. 1 as illustrated in Fig. 6 by the increasing voltage curve 28 and the decreasing voltage curve 29. These curves represent the relationship between the values of output reference voltage and the time required for the voltage to attain such values in response to a rapid movement of the potentiometer slider from one extreme position to the other. It will be noted that the characteristics represented by these curves are almost, but not quite, exactly linear. Like Fig. 1, the modification of Fig. 2 has the advantage that the rate of change of output reference voltage in response to small incremental movements of the slider is always the same irrespective of the value of the reference voltage at the beginning of the change.

A further advantage of the modification of Fig. 2 is that because of the substantial reduction of the variable direct component which results from eliminating the potentiometer from the charging and discharging circuits, the constant alternating charging component can be substantially reduced in magnitude. Consequently, the size of the capacitor can be reduced to 25 percent or less of the size of the capacitor required in the circuit of Fig. l or alternatively the resistors 12 and 12a may be correspondingly reduced in size.

The modification of Fig. 2 may be used in all applications in which a high degree of linearity is required. A small amount of non-linearity remaining in the characteristics is due to the change of the control electrode direct voltage bias of cathode follower valve 21 which is required to vary the voltage of the output terminal 13 through the range of O to 100 volts positive. This change in bias is small and is of the order of 5 to 8 volts.

For applications in which almost mathematically exact linearity of the characteristics is desirable, the effect of the change in bias of the cathode follower amplifier stage may be compensated by the addition of a second stage cathode follower amplifier which counteracts the effect of such change in bias, such as illustrated in the modification of Fig. 3. In this modification, the alternating voltage terminal 19 is disconnected from the output terminal 13 and is connected to the anode terminal 36a of a second cathode follower valve of which the anode is connected through a resistor 31 to the output terminal 13 and the cathode is connected through a cathode follower resistor 32 to the junction point of two resistors 33 and 34, which together with the resistor 35 constitute the cathode follower resistance of the first stage valve 21. The control electrode 3% is connected to a point of fixed voltage on a voltage divider comprising a pair of resistors 36 and 37 connected in series relationship with each other across the O and 160 volts negative supply terminals 4 and 2.

In order to eliminate the direct voltage bias component, it is necessary to maintain the voltage of the terminal 19 at all times equal to the voltage of the point 14, i. e. the voltage of the negative terminal of the capacitor 6. This is accomplished in the following manner: As the voltage of point 14 is caused to vary between 100 volts and 0, the voltage of output terminal 13 will follow along except that in the absence of the second stage cathode follower the relationship of its voltage to the voltage of point 14 will differ throughout the range of output voltages by the amount of change in bias required by valve 21 to vary the output voltage through such range. Valve 30 operates to cause the current in cathode follower resistor 32, by cathode follower action, to increase in proportion to a decrease in the output voltage across terminals 3 and 13, i. e. an increase of the voltage of terminal 13 in the positive direction. This same current flowing in resistor 31 causes a decrease in the voltage at terminal 30a in proportion to the positive increase of the voltage of output terminal 13. This voltage decrease at the terminal 30a is in the correct direction to oppose the change in bias at the terminal 13 required for difierent values of output voltages throughout the range. Consequently, the voltage at the point 19 is held in approximately fixed relationship with respect to the voltage of the terminal 14 irrespective of the value of the output.

The exact linear relationship between changes in the reference voltage and the time required to effect such changes in response to sudden movements of the slider 5a from one extreme position to the other is shown by the increasing reference voltage curve 38 and the decreasing reference voltage curve 39 of Fig. 7.

The modification of Fig. 4 is the same as Fig. 1 except that the constant component of charging voltage is direct instead of alternating and is supplied from a suitable source of direct voltage which is preferably an insulated rectifier but which in the interest of simplicity is illustrated as two batteries 40 and 41 of equal voltage connected in series relationship. The voltage of the batteries may have any suitable value. For the purpose of illustration, the voltage of each battery may be assumed to be volts. As shown, the common point of the two batteries is connected to the point 15 and to the slider 5a of the potentiometer, the positive terminal of battery 40 is connected through the discharge circuit resistor 12 to the anodes of valves 8 and 9 and the negative terminal of battery 41 is connected through charging circuit resistor 12a to the cathodes of valves 10 and 11.

The charging circuit is traced from the positive terminal of battery 41 to slider 5a of the potentiometer through the active portion of the potentiometer to the positive terminal of capacitor 6, and from the negative terminal of the capacitor through valve 10 and charging circuit resistor 12a to the negative terminal of the battery. Similarly, the discharge circuit is traced from the positive terminal of battery 40 through discharge circuit resistor 12 and valve 8 to the negative terminal of capacitor 6 and from the positive terminal of the capacitor through the active portion of the potentiometer to the slider 5a and thence to the negative terminal of battery 40.

The operation is as follows:

An initial equilibrium condition is assumed in which the slider a is at some intermediate point on the potentiometer such as the 50 volt point and the voltage on the capacitor is 50 volts. In other words, the voltages of the points 14 and 15 are equal.

The series connected valves 8 and complete a local circuit across the battery terminals and the series connected valves 9 and 11 complete a parallel local circuit, and a current flows in each of these local circuits. The voltage drop across each of the valves when conducting may be considered to be approximately 1 volt. It is not uniform for all valves. Consequently, the currents in the two local circuits may be unequal as a result of non-uniformity of the valve characteristics. The. differ ence between the battery voltage and the valve voltage drops in the local circuits is absorbed by the resistors 12 and 12a. In the equilibrium condition, no current flows in the capacitor circuit and thus no charge is added to or removed from the capacitor. The reference voltage at the output terminals will be 50 volts plus a relatively small bias voltage between the grid 21a and the cathode 210.

If it is desired to change the reference voltage to a higher value; e. g., 75 volts, the slider 5a is moved downward to the 25 volt point on the potentiometer. Since the capacitor voltage cannot change instantaneously, the point immediately becomes 25 volts more negative than the point 14. Consequently, the cathode voltage of valve 9 and the anode voltage of valves 8, 9 and 11 are immediately lowered 25 volts. The result is that the anodes of valves 8 and 11 become 24 volts more negative than their cathode and valves 8 and 11 cease conducting.

However, the valve 10 continues to conduct and charge the capacitor. The total voltage which is active in the charging direction at the instant of moving the slider to the 25 volt point is the voltage of battery 41; i. e., 100 volts plus the voltage of the active portion of the potentiometer; i. e., 75 volts minus the voltage on the capacitor; i. e., 50 volts. Thus the net charging voltage is seen to be equal to the sum of the constant battery voltage component plus the difference between the potentiometer voltage and the voltage on the capacitor. This difference voltage decreases as the voltage on the capacitor increases during the charge. Consequently, it is a variable component, and the net charging voltage is thus seen to be the sum of a constant component and a variable component which at the beginning of the charge is 125 volts. As the charge on the capacitor increases, the voltage of point 14 becomes increasingly negative and finally becomes equal to the voltage of the point 15, and the voltage on the capacitor becomes equal to the voltage between the terminal 3 and the slider 5a; i. e., 75 volts. When this condition is reached, the voltages of the cathodes of valves 8 and 11 have been lowered 25 volts and consequently, each of these cathodes is again 1 volt negative with respect to its anode and conduction is reestablished in valves 8 and 11. Currents again flow in the local circuits through valves 8 and 10 in series and valves 9 and 11 in series. Current ceases to flow in the capacitor circuit. Thus the initial condition of equilibrium is reestablished. During the charging period, the variable component of the charging voltage approached and became equal to zero with the result that at the end of the charging period the constant battery voltage component was.

the net charging voltage. The voltage across the capacitor is reproduced at the output terminals 3 and 13 as the reference voltage by cathode follower operation of electric valve 21 and cathode resistor 24.

If it is desired to decrease the reference voltage to 25 volts, the slider 5a is moved upward to the 75 volt point on the potentiometer. As a result, the point 15 is immediately made 50 volts more positive than point 14, since the Voltage on the capacitor cannot change instantaneously. Consequently, the anode and cathode of valve 11 and the cathodes of valves 9 and 10 are made 50 volts more positive. As a result, the cathodes of valves 9 and 10 become 49 volts positive with respect to their anodes and valves 9 and 10 cease conducting. The valve 8 continues to conduct and discharges the capacitor 6. During the discharge period, the net discharging voltage is the sum of the constant component voltage of battery plus a variable component which is the difference between the voltage on the capacitor and the voltage between the terminal 3 and slider 5a.

As the capacitor discharges, its voltage decreases and the voltage of point 14 approaches and becomes equal to the voltage of the point 15 and the voltage on the capacitor is decreased to 25 volts. When this condition is reached, the voltages of the anodes of valves 9 and 10 have again become 1 volt more positive than their cathodes and as a result, valves 9 and 10 resume conduction to reestablish the initial equilibrium condition and terminate the discharge of the capacitor. The cathode follower amplifier valve 21 and cathode resistor 24 continuously reproduce the capacitor voltage as the reference voltage at the output terminals 3 and 13.

The output reference voltage versus time characteristic of the modification of Fig. 4 is similar to that of Fig. 1 as illustrated by the curves 25 and 26 of Fig. 5.

Although in accordance with the provisions of the patent statutes this invention is described as embodied in concrete form and the principle thereof has been explained together with the best mode in which it is now contemplated applying that principle, it will be understood that the elements shown and described are merely illustrative and that the invention is not limited thereto since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of this invention or from the scope of the annexed claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A timed adjustable reference voltage unit comprising a pair of output terminals providing a source of variable direct voltage, a capacitor having connections to said terminals, a source of variable direct input voltage, a source of voltage of constant magnitude, a charging circuit for said capacitor including said constant magnitude voltage source and one of said variable direct voltage sources, and electric valve means in said circuit and connected to be responsive to the difference between said capacitor voltage and said input voltage for determining the rate of change of direct voltage on said capacitor.

2. A timed adjustable reference voltage unit comprising a pair of output voltage terminals providing a source of variable direct reference voltage, a capacitor having connections to said terminals, a source of variable direct input control voltage, a source of constant voltage, charging and discharging circuits for said capacitor each including said constant voltage source and one of said variable direct voltage sources connected in series relationship, and electric valve means in each of said circuits connected to be responsive to the difference of said input voltage and the voltage of said capacitor for utilizing said constant voltage source to render substantially uniform the rate of change of direct voltage on said capacitor and at said output terminals in response to variation of said direct input voltage.

3. A timed reference voltage unit comprising a pair of output terminals providing a source of variable direct reference voltage, a capacitor having connections to said terminals, charging and discharging circuits for said capacitor having a common portion, a source of variable input control voltage and a source of voltage of constant magnitude connected in series relationship with each other in said common portion, and a separate electric valve in each of the independent portions of said circuits having connections to said capacitor and to said direct input voltage source and responsive to a difference between said input voltage and the voltage of said capacitor for utiliz ing said constant voltage source to render substantially uniform the rate of change of said capacitor voltage and of said output reference voltage in response to variation of said input voltage.

4. A timed reference voltage unit comprising a pair of output voltage terminals providing a source of variable direct reference voltage, a capacitor having connections to said terminals, a source of variable direct input control voltage, a source of constant voltage, charging and discharging circuits for said capacitor each including said constant voltage source and one of said variable direct voltage sources connected in series relationship, a separate electric valve connected in each of said circuits, and additional electric valve means having connections to said capacitor and said direct input voltage source and responsive to the difference between said input voltage and the voltage on said capacitor for controlling said separate electric valves and said constant voltage source to change the voltage on said capacitor at a substantially uniform rate to equalize the direct voltage on said capacitor with said direct input voltage.

5. An adjustable reference voltage unit comprising a pair of output voltage terminals, a capacitor having connections to said terminals, a charging circuit for said capacitor, a source of variable direct voltage and a source of voltage of constant magnitude connected in series relationship with each other in said circuit, and electric valve means connected in said circuit and responsive to the magnitude of said variable direct voltage for rendering said constant voltage effective to change the voltage on said capacitor.

6. An adjustable reference voltage unit having output voltage terminals, a pair of direct voltage supply terminals, a potentiometer connected across said supply terminals and having a movable contact, a capacitor connected in circuit between said movable contact and said output terminals, charging and discharging circuits for said capacitor, a pair of alternating voltage terminals connected to said charging and discharging circuits for supplying an alternating voltage thereto, and separate electric valves in each of said circuits responsive to the voltage change produced by movement of said movable contact in opposite directions from an intermediate position on said potentiometer for selectively energizing said circuits to vary the direct voltage on said capacitor at a substantially constant rate determined primarily by the magnitude of said alternating voltage.

7. An adjustable reference voltage unit having output voltage terminals, a pair of direct voltage supply terminals, a potentiometer connected across said supply terminals and having a movable contact, a capacitor connected in circuit between said movable contact and said output terminals, a bridge network, connections from diametrically opposite terminals of said bridge network to said movable contact and to said capacitor, charging and discharging circuits for said capacitor connected to the remaining terminals of said bridge network, a pair of alternating voltage terminals connected to said charging and discharging circuits for'supplying alternating voltage thereto, and a separate rectifying device in each arm of said bridge network responsive to movement of said movable contact in opposite directions from an intermediate position on said potentiometer to selectively initiate conduction in said charging and discharging circuits thereby to vary the direct voltage on said capacitor at a substantially constant rate.

8. A timed adjustable reference voltage unit having output voltage terminals, a pair of direct voltage supply terminals, a potentiometer connected across said supply terminals and provided with a movable contact, a capacitor connected in circuit between said potentiometer and said output terminals and having one terminal connected to a terminal of said potentiometer, a plurality of electric valves connected to form a bridge network, connections from diametrically opposite terminals of said bridge network to the other terminal of said capacitor and to said movable contact, capacitor charging and discharging circuits connected to the remaining terminals of said bridge network, a transformer having its secondary winding connected to said circuits for supplying an alternate voltage thereto, said valves being responsive to the voltage change produced by movement of said movable contact in opposite directions from an intermediate position on said potentiometer for selectively initiating flow of current in said charging and discharging circuits thereby to vary the direct voltage on said capacitor at a substantially constant rate.

9. An adjustable reference voltage unit having output voltage terminals, a pair of direct voltage supply terminals, a potentiometer connected across said supply terminals and provided with a movable contact, a capacitor connected in circuit betweensaid potentiometer and said output terminals, a plurality of electric valves connected in a bridge network, connections from diametrically opposite terminals of said network to said capacitor and to said movable contact, a capacitor charging circuit including one of said valves and a portion of said potentiometer connected in series relationship, a discharging circuit for said capacitor including a second one of said valves and a portion of said potentiometer connected in series relationship, a transformer having a secondary winding connected to supply alternating voltage to said charging and discharging circuits, said electric valves being responsive to adjustment of said movable contact to determine the voltage charge of said capacitor.

10. An adjustable reference voltage unit comprising in combination a pair of direct voltage supply terminals, a potentiometer connected across said terminals and having a movable contact, a capacitor having one terminal connected to one terminal of said potentiometer, four electric valves connected in a bridge network, connections from diametrically opposite points of said network to said movable contact and to the other terminal of said capacitor, a charging circuit for said capacitor including one of said valves and a portion of said potentiometer connected in series relationship, a discharging circuit for said capacitor including a second of said electric valves and a portion of said potentiometer, a pair of alternating voltage supply terminals connected to said charging and discharging circuits for supplying an alternating voltage thereto to render substantially constant the rate of change of direct voltage on said capacitor, a cathode follower circuit having output terminals across which the reference voltage appears and comprising an electric valve provided with an anode, a cathode and a control electrode, a cathode follower resistor connected in circuit with said cathode, and connections from the terminals of said capacitor to said cathode and control electrode.

11. A timed adjustable reference voltage unit having output terminals, a pair of direct voltage supply terminals, a potentiometer connected across said supply terminals and provided with a movable contact, a capacitor connected in circuit between said potentiometer and said output terminals, a bridge network, a separate electric valve connected in each arm of said bridge network, connections from diametrically opposite terminals of said bridge network to said movable contact and to said capacitor, capacitor charging and discharging circuits connected to the remaining terminals of said bridge network, a transformer having its secondary winding connected in said charging and discharging circuits between said remaining terminals of said network and said movable contact to effect a substantially uniform rate of change of voltage charged on said capacitor, a cathode follower circuit having output terminals across which the reference voltage appears and comprising an electric valve provided with an anode, a cathode and a control electrode, a cathode follower resistor connected in circuit with saidcathode, and connections from the terminals of said capacitor to said cathode and control electrode.

12. A timed adjustable reference voltage unit comprising a pair of direct voltage supply terminals, a pair of output voltage terminals across. which the reference voltage appears, a cathode follower circuit for supplying said reference voltage to said output terminals comprising an electric valve having an anode, a cathode and a control electrode, a connection from said anode to one of said directvoltage terminals, a cathode follower resistor connected between said cathode and the other of said direct voltage terminals, a potentiometer having connections to said direct voltage terminals, and having a movable contact, a capacitor having connections to said control electrode and one of said output terminals, a bridge network, a separate electric valve connected in each arm of said bridge network, connections from diametrically opposite terminals of said bridge network to said capacitor and to said movable contact, capacitor charging and discharging circuits connected to the remaining terminals of said bridge network, a pair of alternating voltage supply terminals and a transformer having a primary winding connected across said alternating voltage terminals and a secondary winding connected to said charging and discharging circuits between said remaining terminals and said movable contact to render substantially constant the rate of change of direct voltage on said capacitor.

13. An adjustable reference voltage unit having output voltage terminals across which the direct reference voltage appears, a pair of direct voltage supply terminals, a potentiometer connected across said supply terminals and provided with a movable contact, a capacitor connected in circuit between said potentiometer and said output terminals, four electric valves connected in a bridge network, connections from diametrically opposite terminals of said bridge network to said movable contact and to said capacitor, capacitor charging and discharging circuits connected to the remaining terminals of said bridge network, and a transformer having its secondary winding connected in said charging and discharging circuits between said remaining terminals of said bridge network and one of said output terminals to effect a substantially uniform rate of change of direct voltage on said capacitor.

14. A timed adjustable reference voltage unit comprising a piar of direct voltage supply terminals, a pair of output voltage terminals across which the direct reference voltage appears, a cathode follower circuit for supplying voltage to said output terminals comprising an electric valve having an anode, a cathode and a control electrode, a connection from said anode to one of said direct voltage terminals, a cathode follower resistor connected between said cathode and the other of said direct voltage terminals, a potentiometer having connections to said direct voltage terminals, and a movable contact adjustable to define and vary an active portion of said potentiometer, a capacitor having connections to said control electrode and to one of said output terminals, a connection from one terminal of said capacitor to the terminal of said potentiometer at the end of said active portion, a bridge network, a separate electric valve connected in each arm of said network, connections from diametrically opposite terminals of said bridge network to said capacitor and said movable contact, capacitor charging and discharging circuits connected to the remaining terminals of said network, a pair of alternating voltage supply terminals and a transformer having a primary winding connected across said alternating voltage terminals and having a secondary winding connected in said charging and discharging circuits between said remaining terminals and one of said output terminals, said separate electric valves being responsive to the difference in the voltage across said capacitor and the voltage across said active portion of said potentiometer to initiate and terminate flow of current in said charging and discharging circuits to vary the voltage charged across said capacitor at a substantially constant rate.

15. An adjustable reference voltage unit a source of direct voltage comprising a pair of direct voltage supply terminals, a pair of output voltage terminals across which the direct reference voltage appears, a cathode follower circuit for supplying voltage to said output terminals comprising an electric valve having an anode, a cathode and a control electrode, a connection from said anode to one of said direct voltage terminals, a cathode follower resistor connected between said cathode and the other of said direct voltage terminals, a second stage cathode follower circuit comprising a second electric valve having an anode and a cathode connected to intermediate points on said cathode follower resistor and having a control electrode connected to an intermediate voltage point of said source, a potentiometer having connections to said direct voltage terminals and a movable contact adjustable to define and vary an active portion of said potentiometer, a capacitor having connections to said control electrode of said first valve and to one of said output terminals, a connection from one terminal of said capacitor to the end of said active portion, a bridge network, a separate electric valve connected in each arm of said network, connections from diametrically opposite terminals of said bridge network to said capacitor and said movable contact, capacitor charging and discharging circuits connected to the remaining terminals of said network, a pair of alternating voltage supply terminals and a transformer having a primary winding connected across said alternating voltage terminals and having a secondary winding connected in said charging and discharging circuits between said remaining terminals and a point in the anode-cathode of said second electric valve, said separate electric valves being responsive to the difference in the voltage across said capacitor and the voltage across said active portion of said potentiometer to initiate and terminate flow of current in said charging and discharging circuits thereby to vary the direct voltage across said capacitor at a substantially uniform rate.

16. An adjustable reference voltage unit comprising a pair of output voltage terminals, a pair of direct voltage supply terminals, a potentiometer connected across said supply terminals and having a movable contact, a capacitor connected in circuit between said movable contact and said output terminals, charging and discharging circuits for said capacitor, a source of direct voltage of constant magnitude connected to said movable contact and to said circuits for supplying direct voltage thereto, and electric valve means responsive to movement of said movable contact in opposite directions from an intermediate position on said potentiometer for selectively initiating current flow in said circuits to vary the charge on said capacitor at a substantially constant rate.

17. In a circuit for controlling the rate of change of voltage across a capacitor, a source of variable direct input voltage having one terminal connected to one terminal of said capacitor, and voltage control means including a source of substantially constant voltage and electric valve means coupling the other terminal of said input voltage source to the other terminal of said capacitor, said electric valve means connecting said constant voltage source in voltage controlling relation with said capacitor only in response to deviation between said input voltage and the voltage of said capacitor.

18. In a circuit for controlling the rate of change of voltage across a capacitor, a source of variable direct input voltage having one terminal connected to one terminal of said capacitor, means including a source of substantially constant voltage coupling the other terminal of said input voltage source to the other terminal of said capacitor, and electric valve means responsive to deviation between the voltage of said capacitor and said input voltage for rendering said constant voltage source effective to vary the charge on said capacitor at a substantially uniform rate determined primarily by the magnitude of said constant voltage.

19. In a circuit for controlling the rate of change of voltage across a capacitor, 21 source of variable direct input voltage having one terminal connected to one terminal of said capacitor, and electric valve means including a source of substantially constant voltage coupling the other terminal of said input voltage source to the other terminal of said capacitor, said valve means connecting said constant voltage source in aiding relation with any change in said input voltage from a predetermined normal value thereby to increase the voltage available for changing the charge on said capacitor.

References Cited in the file of this patent UNITED STATES PATENTS 2,176,742 LaPierre Oct. 17, 1939 2,446,188 Miller Aug. 3, 1948 2,465,809 Lavender Mar. 29, 1949 2,471,835 Norgaard May 31, 1949 2,521,058 Goldberg Sept. 5, 1950 

